A "Boudreaux Back Rub" is when you are standing or walking, and a chick jumps on you from behind, pulls out your cock, and starts to give you a handjob from the piggyback position. It's named after the genius who conjured this move up in an inspired dream...

Dude, I was just walking to the bar and she came out of nowhere like a ninja and gave me a Boudreaux Back Rub... it was totally tits!!!